1. Field of the Invention
The present invention relates to a vibration type actuator and a vibration type driving apparatus, respectively utilizing vibrations.
2. Related Background Art
As a vibration type actuator for producing a motion about a multi-axis, a spherical vibration type actuator has been proposed as disclosed, for example, in Journal of Seimitsu Kougaku Kai, Vol. 61, No. 3, pp. 1227-1230, 1995 or NIKKEI MECHANICAL, No. 5, pp. 26-27, Apr. 28, 1997.
Such a spherical vibration type actuator rotates a spherical moving member (rotor) about two axes or three axes among three axes intersecting at a right angle. A plurality of vibration members (stators) each producing a rotation force about one axis by using vibrations (e.g., travelling waves) are disposed in pressure contact with the moving member.
Such spherical vibration type actuators now under development include a two-degree of freedom type using four vibration members and a three-degree of freedom type using three vibration members.
An example of the vibration member used by a spherical vibration type actuator is a vibration member of a ring vibration type actuator used for driving an auto focus lens of a camera. FIG. 16 is a perspective view of this vibration member. The vibration member 19 has a ring elastic member 19a whose bottom is formed with piezoelectric elements 9b made of piezoelectric ceramic. The piezoelectric elements are formed with two-phase driving elements having a proper phase difference (an odd number multiple of a half wave). These two-phase driving elements are driven by alternating signals having a proper phase difference (e.g., 90xc2x0), so that flexural (bending) travelling waves are formed in the elastic member 19a along its circumferential direction. An unrepresented contact member is made in contact with the elastic member 19a by unrepresented pressure means, so that the contact member and vibrating member are provided with a relative motion along the direction opposite to the direction of travelling waves. If the vibrating member 19 is fixed, the contact member rotates as the moving member.
In a spherical vibration type actuator, for example, in a two-degree of freedom type spherical vibration actuator such as shown in FIG. 17, two pairs of opposing vibrating members 19 are disposed around a spherical moving member 2 to realize a two-degree of freedom motion by using the center lines of the vibrating members 19 as rotation axes.
As another example of the vibration type actuator producing a motion about a multi-axis, a piezoelectric manipulator has been proposed as described in a paper pp. V9-K15, Third International Conference on Motion and Vibration Control, Chiba, Sep. 1, 1996. The structure of this piezoelectric manipulator is shown in FIG. 18.
As shown, the piezoelectric manipulator is constituted of a vibration member 19 and semispherical moving members 20a and 20b mounted on the vibration member 19 at opposite ends thereof along its axial direction. The vibration member 19 is constituted of a cylindrical elastic member and piezoelectric elements. Unrepresented divided electrodes are formed around the vibration member 19. The semispherical moving members 20a and 20b are attracted toward each other by a spring 21 provided in the vibration member 19, so that the vibration members 20a and 20b are always in contact with the opposite opening ends of the vibration member 19.
By applying proper alternating signals to the divided electrodes so as to adjust vibrations to be excited by the vibration member 19, the semispherical moving members 20a and 20b in contact with the opening ends of the vibration member 19 are driven by the single vibrating member 19.
According to the drive principle, an ellipsoidal motion is formed at contact points between the semispherical moving members 20a and 20b and the vibration member 19. By changing an alternating voltage applied to each electrode, ellipsoidal motions in a plurality of motion planes are formed so that the semispherical rotors can be driven in desired directions.
However, since the conventional spherical vibration type actuator shown in FIG. 17 has a plurality of vibrating members, the following disadvantages have been reported to date.
(1) Since a plurality of vibration members are used for a rotation about one axis, it is necessary to make each vibration member have the same characteristics.
(2) Since a plurality of vibration members exist along the circumference of the moving member, it is difficult to make the actuator compact and a space efficiency is poor.
(3) Since the vibration member for another axis not contributing to vibrations is made in pressure contact with the moving member, a resistance to rotation is generated and a problem of efficiency and heat generation occurs.
For the conventional vibration type actuator having a tubular vibration member shown in FIG. 18, the following disadvantages have been reported.
(1) Since alternating signal matching drive directions are required to be applied to a plurality of electrodes formed on the circumferential area of the vibration member, the signal becomes different for each electrode and the control becomes complicated.
(2) Since the semispherical moving members 20a and 20b are made in pressure contact with the cylindrical vibration member 19 by pulling the moving members 20a and 20b toward each other by the spring 21, the movable area is limited and the pressure force is not uniform and is difficult to be adjusted.
According to one aspect of the present invention, a vibration type actuator is provided which comprises a vibration member formed with vibration generating means for generating vibration displacements at least in three different directions wherein a relative motion in a desired direction is generated between the vibration member and a contact member in contact with the vibration member by supplying the vibration displacements in the three directions to impart synthetic vibrations to the vibration member.
It is an object of the invention to generate a driving force of a multi-degree of freedom by using a single vibration member.